It is known that, for the color development of a silver halide color photographic material, after exposure, an oxidized aromatic primary amine color developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green, and red light, and yellow, magenta, and cyan color image formers, which are respectively the complementary colors of blue, green, and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a phenolic type coupler, such as phenols and naphthols, is generally used for forming a cyan color image.
Color couplers must satisfy various requirements. For instance, it is necessary that they have a good spectral property and provide a dye image by color development, having excellent stability to light, temperature, and humidity for a long period of time.
It is also required in a multilayer color photographic light-sensitive material that couplers are fixed in respective layers separated from each other, in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. According to such a method, couplers are solubilized to alkali, and then they are added to an aqueous gelatin solution, or the couplers are dissolved in an organic solvent having a high boiling point, and then they are dispersed in an aqueous gelatin solution, since the couplers are immiscible with an aqueous gelatin solution. Such color couplers may cause crystal formation in a photographic emulsion. Furthermore, when using an organic solvent having a high boiling point, a large amount of gelatin must be employed, since the organic solvent having a high boiling point makes an emulsion layer soft. Consequently, this increases the thickness of the material even though it is desirable to reduce the thickness of the emulsion layer.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler latex obtained by polymerization of a monomeric coupler. An example of a method of adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino-silver halide emulsion and a method in which an oleophilic polymer coupler obtained by polymerization of a monomeric coupler is dispersed in a latex form in an aqueous solution. Some examples of the former emulsion polymerization methods include an emulsion polymerization method in an aqueous gelatin phase, as described in U.S. Pat. No. 3,370,952, and an emulsion polymerization method in water, as described in U.S. Pat. No. 4,080,211. An example of the latter method in which an oleophilic polymer coupler is dispersed in a latex form in gelatin is described in U.S. Pat. No. 3,451,820.
The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, the deterioration of strength of the film formed is small, because the hydrophobic substance is in a latex form. Also, since the latex can contain monomeric unit of couplers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the increase of viscosity is small. Furthermore, color mixing is prevented, since a polymer coupler is completely immobilized and the crystallization of couplers in the emulsion layer is small.
With respect to the addition of these polymer couplers in a latex form to a gelatino-silver halide emulsion, magenta polymer coupler latexes are described, for example, in U.S. Pat. No. 4,080,211, British Pat. No. 1,247,688, U.S. Pat. Nos. 3,451,820, and 3,926,436 West German Pat. No. 2,725,591, etc.